1. Field of the Invention
The present invention relates to the field of fluid containers. More specifically, the present invention relates to fluid containers with self-insulating side walls.
2. Background Information
A number of beverage containers having self-insulating side walls formed with air spaces disposed in between the innermost and outermost layers are known in the art. See e.g. U.S. Pat. Nos. 5,752,653 and 5,542,599. The insulating air spaces of these prior art beverage containers are pre-formed between the layers at manufacturing time. These prior art containers suffer at least the disadvantage in that because of the pre-formed air spaces, the side walls take up more space than the side walls of conventional non-self-insulating beverage containers, resulting in the self-insulating beverage containers being less stackable than the conventional non-self-insulating beverage containers. The stacking attribute is a very important attribute for hot beverage cups. It is essential to allowing large quantities of these hot beverage cups to be produced, packaged and transported together.
Thus, a self-insulating container that can provide similar insulating advantage, but without compromising the stacking ability of the container is desired.
A fluid container having a novel thermally responsive side wall is disclosed. The side wall is constituted of multiple layers that thermally respond to the presence of fluid of at least a predetermined temperature in the fluid container in a coordinated manner. In one embodiment, the coordinated thermal response either creates or increases insulating air space between an innermost and an outermost one of the layers. In another embodiment, the coordinated thermal response increases insulation of an intermediate layer between an innermost and an outermost one of the layers.